Guided-mode resonance (GMR) is an effect in optical physics wherein the guided modes of an optical waveguide can be excited and simultaneously extracted, re-radiated, by the inclusion of a phase-matching element, such as a diffraction grating, in the structure. Such modes are also called “leaky modes,” since they do not remain guided but instead can be extracted from the waveguide. Thus, GMR effects can arise via quasi-guided or “leaky” waveguide modes induced on patterned films with subwavelength periods.
The Rayleigh anomaly in optical physics arises on periodic surfaces illuminated by incident electromagnetic waves. Specifically, the “Rayleigh anomaly” refers to the appearance or disappearance of diffracted spectral orders under a variation of the input light frequency or angle. At the transition point between propagating and evanescent orders, characteristic “kinks” appear in the spectra. This effect has been widely regarded as substantially useless or even as a nuisance for many optical applications. For example, the effect can be problematic or troublesome when diffraction gratings are used in the spectroscopic analysis of atomic absorption processes in a medium of interest.
Moreover, the concepts of GMR and the Rayleigh anomaly have not previously been connected or coupled for optical applications. Therefore, there exists a need for improved optical devices capable of productively harnessing the Rayleigh anomaly, including in conjunction with GMR effects. There also exists a need for improved uses and applications of such devices.